Ageing and inflammation with focus on end-stage renal diseases : genetic and epigenetic factors

The presence of ageing-associated disorders at a relatively young age in patients suffering from chronic kidney disease (CKD) has led to the hypothesis that CKD is characterized by accelerated ageing, resulting in a marked discrepancy between chronological and biological age. Factors that accelerate biological ageing, such as inflammation, oxidative stress, and toxins, impact the processes of cellular senescence and/or apoptosis, thereby shortening the life span of cells, and consequently, of the organism as a whole. Numerous studies have linked increased cellular senescence and apoptosis to disorders commonly associated with ageing, such as cardiovascular disease (CVD), osteoporosis, and cognitive dysfunction – all of which are common in the uremic phenotype. In Study I, we demonstrate that increased arterial gene expression of cyclin-dependent kinase inhibitor 2A (CDKN2A), a known inducer of cellular senescence, is associated with the presence of CVD and vascular calcification (VC) in CKD patients. Furthermore, there is a positive correlation between CDKN2A expression and the expression of matrix Gla protein (MGP) and runt-related transcription factor 2 (RUNX2), both of which are involved in osteogenesis. We also show a tentative relationship between a higher degree of VC and increasing p16INK4a expression, a cognate protein of CDKN2A. In Study II, we use telomere length as a biomarker of biological age, showing that CKD patients have shorter telomeres than non-CKD controls. In addition, our results indicate a possible association between longitudinal telomere length, folate, and immunosuppressive treatment in patients undergoing renal transplantation (RTx). This suggests that anti- metabolite therapy may have an impact on biological ageing in RTx patients. In Study III, we show that the global methylation status in dialysis and RTx patients at baseline and after 12 months of renal replacement therapy (RRT) differs at several sites in the genome from that of age- and gender-matched healthy controls. Furthermore, differences in methylation between patients and controls can be found at CpG sites located in genes with known functional relevance to CKD, cellular ageing, CVD and/or metabolic disease. Continuing our investigations of factors affecting epigenetic status, Study IV investigates the association between the degree of self-reported physical activity and global DNA methylation in Swedish seniors. In this study, we demonstrate that individuals who reported higher physical activity had less global DNA methylation than those who were less physically active. Study V describes the application of a multifactorial mathematical model for predicting the presence of inflammation in a dataset generated from 225 incident dialysis patients. Eight of the ten features with the highest predictive factor were single nucleotide polymorphisms (SNPs), suggesting a large genetic influence on inflammation in CKD patients. In Study VI, the interplay between inflammatory status, genotype, and mortality is demonstrated in two cohorts of incident dialysis patients. The mortality was reduced in inflamed individuals carrying a 32 base-pair deletion in the C-C motif chemokine receptor 5 (CCR5) gene compared to individuals who were inflamed but lacked the deletion

Increased telomere attrition following renal transplantation: impact of anti-metabolite therapy

Background: The uremic milieu exposes chronic kidney disease (CKD) patients to premature ageing processes. The impact of renal replacement therapy (dialysis and renal transplantation [RTx]) or immunosuppressive treatment regimens on ageing biomarkers has scarcely been studied. Methods: In this study telomere length in whole blood cells was measured in 49 dialysis patients and 47 RTx patients close to therapy initiation and again after 12 months. Forty-three non-CKD patients were included as controls. Results: Non-CKD patients had significantly (P <= 0.01) longer telomeres than CKD patients. Telomere attrition after 12 months was significantly greater in RTx patients compared to dialysis patients (P = 0.008). RTx patients receiving mycophenolate mofetil (MMF) had a greater (P = 0.007) degree of telomere attrition compared to those treated with azathioprine. After 12 months, folate was significantly higher in RTx patients than in dialysis patients (P < 0.0001), whereas the opposite was true for homocysteine (P < 0.0001). The azathioprine group had lower levels of folate after 12 months than the MMF group (P = 0.003). Conclusions: The associations between immunosuppressive therapy, telomere attrition, and changes in folate indicate a link between methyl donor potential, immunosuppressive drugs, and biological ageing. The hypothesis that the increased telomere attrition, observed in the MMF group after RTx, is driven by the immunosuppressive treatment, deserves further attention

CDKN2A/p16INK4a expression is associated with vascular progeria in chronic kidney disease

Patients with chronic kidney disease (CKD) display a progeric vascular phenotype linked to apoptosis, cellular senescence and osteogenic transformation. This has proven intractable to modelling appropriately in model organisms. We have therefore investigated this directly in man, using for the first time validated cellular biomarkers of ageing (CDKN2A/p16INK4a, SA-β-Gal) in arterial biopsies from 61 CKD patients undergoing living donor renal transplantation. We demonstrate that in the uremic milieu, increased arterial expression of CDKN2A/p16INK4a associated with vascular progeria in CKD, independently of chronological age. The arterial expression of CDKN2A/p16INK4a was significantly higher in patients with coronary calcification (p=0.01) and associated cardiovascular disease (CVD) (p=0.004). The correlation between CDKN2A/p16INK4a and media calcification was statistically significant (p=0.0003) after correction for chronological age. We further employed correlate expression of matrix Gla protein (MGP) and runt-related transcription factor 2 (RUNX2) as additional pathognomonic markers. Higher expression of CDKN2A/p16INK4a, RUNX2 and MGP were observed in arteries with severe media calcification. The number of p16INK4a and SA-β-Gal positive cells was higher in biopsies with severe media calcification. A strong inverse correlation was observed between CDKN2A/p16INK4a expression and carboxylated osteocalcin levels. Thus, impaired vitamin K mediated carboxylation may contribute to premature vascular senescence

CDKN2A/p16INK4a expression is associated with vascular progeria in chronic kidney disease

Patients with chronic kidney disease (CKD) display a progeric vascular phenotype linked to apoptosis, cellular senescence and osteogenic transformation. This has proven intractable to modelling appropriately in model organisms. We have therefore investigated this directly in man, using for the first time validated cellular biomarkers of ageing (CDKN2A/p16INK4a, SA-β-Gal) in arterial biopsies from 61 CKD patients undergoing living donor renal transplantation. We demonstrate that in the uremic milieu, increased arterial expression of CDKN2A/p16INK4a associated with vascular progeria in CKD, independently of chronological age. The arterial expression of CDKN2A/p16INK4a was significantly higher in patients with coronary calcification (p=0.01) and associated cardiovascular disease (CVD) (p=0.004). The correlation between CDKN2A/p16INK4a and media calcification was statistically significant (p=0.0003) after correction for chronological age. We further employed correlate expression of matrix Gla protein (MGP) and runt-related transcription factor 2 (RUNX2) as additional pathognomonic markers. Higher expression of CDKN2A/p16INK4a, RUNX2 and MGP were observed in arteries with severe media calcification. The number of p16INK4a and SA-β-Gal positive cells was higher in biopsies with severe media calcification. A strong inverse correlation was observed between CDKN2A/p16INK4a expression and carboxylated osteocalcin levels. Thus, impaired vitamin K mediated carboxylation may contribute to premature vascular senescence

Longitudinal genome-wide DNA methylation changes in response to kidney failure replacement therapy

Chronic kidney disease (CKD) is an emerging public health priority associated with high mortality rates and demanding treatment regimens, including life-style changes, medications or even dialysis or renal transplantation. Unavoidably, the uremic milieu disturbs homeostatic processes such as DNA methylation and other vital gene regulatory mechanisms. Here, we aimed to investigate how dialysis or kidney transplantation modifies the epigenome-wide methylation signature over 12 months of treatment. We used the Infinium HumanMethylation450 BeadChip on whole blood samples from CKD-patients undergoing either dialysis (n = 11) or kidney transplantation (n = 12) and 24 age- and sex-matched population-based controls. At baseline, comparison between patients and controls identified several significant (PFDR < 0.01) CpG methylation differences in genes with functions relevant to inflammation, cellular ageing and vascular calcification. Following 12 months, the global DNA methylation pattern of patients approached that seen in the control group. Notably, 413 CpG sites remained differentially methylated at follow-up in both treatment groups compared to controls. Together, these data indicate that the uremic milieu drives genome-wide methylation changes that are partially reversed with kidney failure replacement therapy. Differentially methylated CpG sites unaffected by treatment may be of particular interest as they could highlight candidate genes for kidney disease per se

DNA Hypermethylation and Inflammatory Markers in Incident Japanese Dialysis Patients

Background/Aims: Inflammation is an established mortality risk factor in chronic kidney disease (CKD) patients. Although a previous report showed that uremic Caucasian patients with inflammation had signs of global DNA hypermethylation, it is still unknown whether DNA hypermethylation is linked to inflammatory markers including a marker of bacterial infections in Japanese CKD patients. Methods: In 44 consecutive incident dialysis patients (26 males, mean age 59 ± 12 years) without clinical signs of infection, global DNA methylation was evaluated in peripheral blood DNA using the HpaII/MspI ratio by the luminometric methylation assay method. A lower ratio of HpaII/MspI indicates global DNA hypermethylation. Procalcitonin (PCT), a marker of inflammation due to bacterial infections, was measured using an immunochromatographic assay. Results: The patients were divided into hyper- and hypomethylation groups based on the median value of the HpaII/MspI ratio 0.31 (range 0.29–0.37). Whereas patients in the hypermethylation group had higher ferritin levels [133.0 (51.5–247.3) vs. 59.5 (40.0–119.0) ng/ml; p = 0.046], there were no significant differences in age, gender, diabetes, smoking, anemia or serum albumin levels. However, the HpaII/MspI ratio showed significant negative correlations with PCT (ρ = –0.32, p = 0.035) and ferritin (ρ = –0.33, p = 0.027) in Spearman’s rank test. In a multiple linear regression analysis, PCT and ferritin were associated with a lower HpaII/MspI ratio (R2 = 0.24, p = 0.013). Conclusion: In this study, global DNA hypermethylation was associated with ferritin and, most likely, PCT, suggesting that inflammation induced by subclinical bacterial infection promoted DNA methylation

Prevalence of Periodontitis in Patients with Established Rheumatoid Arthritis: A Swedish Population Based Case-Control Study

<div><p>Introduction</p><p>The possible hypothesis of a link between periodontitis and rheumatoid arthritis (RA), specifically anti-citrullinated protein antibody (ACPA) positive RA, prompted us to investigate the prevalence of periodontitis in the Swedish Epidemiological Investigation of RA (EIRA), a well-characterised population-based RA case-control cohort.</p><p>Methods</p><p>Periodontal status of 2,740 RA cases and 3,942 matched controls was retrieved through linking EIRA with the National Dental Health Registry (DHR), where dental diagnostic- and treatment codes on the adult Swedish population have been registered. Dental records from 100 cases and controls were reviewed to validate the periodontal diagnostic codes in DHR.</p><p>Results</p><p>The reviewed dental records confirmed 90% of the periodontitis diagnoses in DHR among RA cases, and 88% among controls. We found the positive predictive value of periodontitis diagnoses in the DHR to be 89% (95% CI 78 to 95%) with a sensitivity of 77% (95% CI: 65 to 86%). In total, 86% of EIRA participants were identified in DHR. The risk for periodontitis increased by age and current smoking status in both cases as well as controls. No significant differences in prevalence of periodontal disease in terms of gingivitis, periodontitis, peri-implantitis or increased risk for periodontitis or peri-implantitis were observed between RA cases and controls. In addition, there was no difference on the basis of seropositivity, ACPA or rheumatoid factor (RF), among patients with RA.</p><p>Conclusions</p><p>Our data verify that smoking and ageing are risk factors for periodontitis, both in RA and controls. We found no evidence of an increased prevalence of periodontitis in patients with established RA compared to healthy controls, and no differences based on ACPA or RF status among RA subjects.</p></div

Prevalence of periodontitis in relation to age.

<p>Prevalence (%) and numbers of exposed participants with periodontitis in different age groups identified in DHR demonstrating, (<b>A)</b> RA cases versus controls, (<b>B)</b> ACPA-positive versus ACPA-negative RA patients, (<b>C)</b> RA-women versus RA-men, (<b>D)</b> control-women versus control-men. Statistical differences were observed with increased age for both RA cases and controls. The differences between the groups were analysed by chi-square test or Fisher´s exact test. p-value < 0.05 was considered statistically significant.</p

EIRA RA cases and controls with periodontal diagnostic codes identified in DHR, in relation to ACPA and RF status.

<p>EIRA RA cases and controls with periodontal diagnostic codes identified in DHR, in relation to ACPA and RF status.</p

Association between periodontal codes and smoking habits among RA cases and controls, as compared to never smokers, stratified by gender.

<p>Association between periodontal codes and smoking habits among RA cases and controls, as compared to never smokers, stratified by gender.</p